At the present time, countries which are subjected to substantially low temperatures during the fall, winter and spring seasons rely mainly on oil, coal or electricity as a means for heating. At the present moment, the dependence on oil for heating furnaces or for generating electricity is creating a problem due to the dependence on industrial countries on major oil producing countries.
The use of electricity as a means for heating creates a problem since electricity cannot be stored and therefore must be produced according to its demands by the consumers. Accordingly, daytime will produce peak demands while nightime will require low demands. In some countries, electricity-producing companies charge a lower rate for electricity consumed at night than for electricity consumed during the daytime or the peak period. Accordingly, in order to take advantage of the availability of electricity at a lower rate during the low peak period heat storage accumulators have been developped. These heat storage accumulators accumulate heat during the night and surrender the accumulated heat during the daytime, thus, decreasing the demand for electricity during the peak hours. It will be readily appreciated that if a larger demand for electricity can be generated during the low demand period, the efficiency of the power plants would be greatly improved.
Presently, most of available heat storage cores are made from olivine. Such cores are known to have high refractoriness properties, good heat storage capacity, good heat conductivity for refractory material, and chemical stability. As an example of a presently available heat storage core, there may be mentioned the product manufactured and sold by A/S Olivin, Aeheim, Norway, under the trademark MAGNOSIL 100. This heat storage core is made from olivine and contains 51% MgO, 40% SiO.sub.2 and 6% Fe.sub.2 O.sub.3.
Though this type of heat storage core presents definite advantages, it would appear that in this period of conservation of energy any improvement in heat storage cores which could increase the efficient use of electricity would make a valuable contribution to the energy problem.
Since the energy absorbed by a heat storage core is in function of its specific heat per unit of volume, the size of the core will thus become a factor which presents certain drawbacks, since such cores must be provided with an insulated cover in order to keep the accumulated heat before it will be withdrawn later for circulation in the areas to be heated when the need will appear. Accordingly, cores made from a material having a too low specific heat per unit of volume have to be relatively large in size in order to store a feasible amount of heat, with a corresponding increase in cost of insulating such cores.
On the other hand, it is known that the chemical composition of calcined chrysotile asbestos tailings is very close in many regards to that of olivine used to manufacture heat storage cores. For example, both contain magnesium oxide, silicon oxide and iron oxide. It is also known that chrysotile asbestos tailings constitute about 95% of all asbestos mined and since there is no practical commercial uses known for these asbestos tailings, the accumulation thereof constitutes and environmental and ecological problem for the populations residing close to asbestos mines.
The following Table I gives an idea of the relative similarity between olivine and chrysotile asbestos tailings.
TABLE I ______________________________________ Calcined chrysotile asbestos tailings Sample Sample Sample Olivine A B C ______________________________________ MgO% 49.0 48.3 46.3 48.7 SiO.sub.2 % 42.0 38.5 41.8 40.0 Fe.sub.2 O.sub.3 % 6.5 12.0 11.3 10.8 Al.sub.2 O.sub.3 0.7 0.7 0.4 0.4 CaO -- 0.1 0.1 0.1 Alcalis -- 0.05 0.06 0.06 Loss on ignition 1.2 -- -- -- ______________________________________
Accordingly, it would appear to be highly desirable to provide modified chrysotile asbestos tailings which would approximate certain of the advantages of olivine in the manufacture of heat storage cores while possessing superior heat storage capacity and thermal conductivity per unit of volume.